FIGS. 6(A) and 6(B) show typical prior art phase shifters among which the phase shifter of FIG. 6(A) is of a passive type including resistors 3 and 4, capacitors 5 and 6 and coils 7 and 8 connected between a power source 1 for entering an input voltage Vin and an output resistor 2 for taking out an output voltage Vout. The phase shifter of FIG. 6(B) is of an active type including resistors 10, 11 and 12, a capacitor 13 and an operational amplifier 14 connected between a power source 1 for entering an input voltage Vin and a takeout terminal 9 for taking out an output voltage Vout. These circuits are shown in "Electronic Filter Design Handbook" of McGraw-Hill, for example.
In the phase shifter of FIG. 6(A), if the following relationship is established: ##EQU1## where R is the value of the resistor 2, the resistors 3 and 4 are R/2, respectively, C is the capacitance of the capacitors 5 and 6, L is the inductance of the coils 7 and 8, and .alpha..sub.0 is a constant fixed by the material, etc., its frequency characteristic Vout/Vin is shown in FIG. 7 in which its amplitude A is uniform, and its phase .theta.(.omega.) becomes: ##EQU2##
In the phase shifter of FIG. 6(B), if the following relationship is established: ##EQU3## where R is the value of the resistor 11, and C is the capacitance of the capacitor 13, its amplitude A is also uniform, and its phase .theta.(.omega.) equals equation (3).
It is more and more desired to incorporate high frequency circuits in an integrated circuit. However, the phase shifter shown in FIGS. 6(A) and 6(B) are not suitable for such a circuit integration. More specifically, the phase shifter of FIG. 6(A) requires coils, but it is difficult to provide in an integrated circuit coils or equivalent circuits operative against high frequency waves. Further, as will be understood from equations (1), (2) and (3), both values L and C must be varied in order to vary the phase, and it is hardly established.
In the phase shifter of FIG. 6(B) requiring the operational amplifier, it is difficult to establish a high level input impedance, a low output impedance, a high gain and other indispensable characteristics of the operational amplifier in high frequency ranges.
Any prior art phase shifters other than those shown in FIGS. 6(A) and 6(B) also require coils or a high level input impedance, and it is difficult to incorporate them in a high frequency integrated circuit.